Simmer pork in water, soy sauce, and sugar for at least 20 minutes (until cooked). *You can boil it up to 45 minutes and it will become more tender and absorb the flavors. Drain.
Batter:
Heat the oil in the skillet.
In a bowl, combine the egg and milk.
In another bowl, whisk together the flour, baking powder, and salt.
Add the dry ingredients to the wet ingredients and beat until smooth.
Dip the pork in the batter and fry (at 360°) until golden brown.
Vegetables:
Cook the vegetables and pineapple in butter for a few minutes, keeping the vegetables crisp.
Arrange the pork and vegetables on a platter and pour the sweet & sour sauce over.
Notes:
Make Ahead: You can cut up the meat and vegetables ahead of time and boil the meat ahead of time too. I would think you could also fry the pork ahead of time then just reheat in a hot oven.